This invention relates to the use of an optical fiber in a laser system for delivering a laser light beam to a site remote from the laser light source. More particularly, the invention relates to such a laser light delivery system employing an optical fiber specially manufactured for coupling high peak power laser pulses from a laser resonator to transmitter optics, and for correcting for "hot" power distributions in the laser light beam to thereby generate from the output of the fiber a homogenous light beam.
There are numerous applications in the prior art which utilize fiber optics for the delivery of high power, i.e., Q-switched laser pulses. The high transmission and mechanical flexibility exhibited by fibers permits high levels of optical transmission through a flexible media of small diameter, if the proper fiber design is implemented. Thus, fiber optics can greatly reduce beam delivery system complexity by replacing bulky mirrors and/or prisms.
A major obstacle to the use of fiber optics has been their power transmission capabilities when employed in a high power transmission environment which often results in optical damage to the silica fiber. The ends of the fibers (glass/air interfaces) are the most susceptible areas for the damage to occur and the damage is frequently caused by "hot spots" present in the beam relative to the small surface area of the fiber end. In addition, depending on the fiber construction, parts of the laser beam can contact potting and clamping materials of the cable at the input end of the fiber and this can result in vaporization of these materials and subsequent deposition on the fiber face. This will produce absorption at the fiber surface which will dramatically lower its damage susceptibility.
Thus, while the prior art envisions using optical fibers in a low power transmission environment, for example, for endoscopic illumination in operations and/or other low power applications such as data communications, up to now there has been no reliable manner of implementing optical fibers in a high power environment. It is an object of the present invention to employ optical fiber systems in a high power environment.
By high power, it is generally understood that this relates to Q-switched laser beams of at least about 175-500 mJ/pulse with an average output energy density ranging from about 35 J/cm.sup.2 up to about 100 J/cm.sup.2 and higher (power densities of 1 MW/cm.sup.2 to 2.2 GW/cm.sup.2 and higher). Similarly, long pulse transmission energies ranging from about 1.0-2.5 J/pulse are considered (200-500 J/cm.sup.2).